1. Technical Field
Exemplary aspects of the present invention relate to a projector having a light source device, an optical modulator arranged on an optical axis of a light beam irradiated by the light source device to modulate the light beam in accordance with image information and form an optical image, and a projection lens that enlarges the optical image formed by the optical modulator and projects the optical image.
2. Related Art
Generally, there has been used a projector for presentations at conferences, academic societies, exhibitions and the like. Such projector includes a light source, an optical modulator arranged on an illumination optical axis of a light beam irradiated by the light source to modulate the light beam in accordance with image information and form an optical image, and a projection lens that projects the optical image formed by the optical modulator in an enlarged manner.
The projector occasionally uses an optical converter that optically converts the incident light beam in order to enhance light utilization efficiency irradiated by the light source and restrict transmission of the unnecessary light beam. As an example of the optical converter, there has been known a polarization plate that only transmits a polarized light in a predetermined direction and absorbs other light beam, as well as a projector using such polarization plate (for instance, see Document 1: JP-A-11-160788, FIG. 5).
The projector disclosed in Document 1 includes three optical modulators and the polarization plate is arranged on the light irradiation side of each optical modulator. To be more specific, as shown in FIG. 7, each polarization plate 443 is arranged such that a center axis C passing through the center of an optical image formation area of the optical modulator and being parallel to an illumination optical axis is aligned with a center axis E of a plane on the light irradiation side of the polarization plate 443. The light beams irradiated from the polarization plates 443 are combined though a dichroic prism 444 and projected in a vertically shifting direction by a projection lens 3 having an optical axis shifted upward relative to the center axis of the optical image formation area of the optical modulator. Incidentally, in the projector disclosed in Document 1, the optical modulator is arranged so that the illumination optical axis is aligned with the center axis C as shown in FIG. 7.
However, as shown in FIG. 7, in the projector disclosed in Document 1, since a lens optical axis A of the projection lens 3 is deviated from the illumination optical axis of the light beam irradiated by the light source, when the planar center of the polarization plate 443 on the light irradiation side is positioned on the center axis C of the optical image formation area of the optical modulator, there is generated on the polarization plate 443 an unnecessary area on which the light beam not to be irradiated from the projection lens as an image is incident, thus the size of the polarization plate being increased beyond necessity.
If the polarization plate is downsized too much in order to eliminate the area on which the light beam not to be irradiated from the projection lens 3 as the image is incident, the effective light beam irradiated from the projection lens 3 as image will occasionally be incident on an end surface which is not a light incident plane of the polarization plate 443. In this case, since the effective light beam incident on the end surface will be reflected to an unexpected direction from the end surface and then projected from the projection lens 3, an unexpected image will be projected other than a desired projection image.